IFN-beta impairs superoxide-dependent parasite killing in human macrophages: evidence for a deleterious role of SOD1 in cutaneous leishmaniasis.

Type I IFNs (IFN-alpha/beta) have only recently gained considerable attention as immunomodulators in nonviral infectious diseases. IFN-beta has been shown to protect, in a NO-dependent manner, against murine Old World leishmaniasis caused by Leishmania major, but data in New World leishmaniasis are lacking. We found that IFN-beta dose-dependently increases parasite burden in Leishmania amazonensis- as well as Leishmania braziliensis-infected human macrophages, independent of endogenous or exogenous NO. However, IFN-beta significantly reduced superoxide release in Leishmania-infected as well as uninfected human macrophages. This decrease in superoxide production was paralleled by a significant IFN-beta-mediated increase in superoxide dismutase 1 (SOD1) protein levels. Additionally, IFN-beta inhibition of leishmanicidal activity was mimicked by SOD1 and antagonized by either pharmacological or small interfering RNA-mediated inhibition of SOD1. Finally, pronounced SOD1 expression in situ was demonstrated in biopsies from New World cutaneous leishmaniasis patients. These findings reveal a hitherto unknown IFN-beta/SOD1 axis in Leishmania infection and suggest that inhibition of SOD-associated pathways could serve as strategy in the treatment of L. amazonensis as well as L. braziliensis infection, major human pathogens.